The invention is based on a current coil, for use in a needle motion sensor for fuel injection valves. In a current coil of this type, which is known from WO 90/06439, a cylindrical coil body is inserted into a corresponding receiving opening of a valve holding body of a fuel injection valve and acts as a needle motion sensor there for detecting the motion of an axially movable valve needle of the fuel injection valve. For this purpose, the end of the coil body oriented toward the valve needle has a metallic coil core inserted into it, which is coaxially encompassed by a coil winding that is mounted onto the coil core. The ends of the coil winding wire are each connected to a respective connecting contact wire which on the other end, has connections for external electric connecting lines. In the known current coil, a wire-guiding body is also provided which is slid onto the connecting contact wires on the coil body and therefore fixes them in position.
The known current coil, however, has the disadvantage that after the coil wire has been wound, the winding wire beginning and the winding wire end must be placed with a tension relief loop against the ends of the connecting contact wires and soldered there. This soldering process therefore requires manual labor that is expensive for technical manufacturing reasons and cannot be automated. Furthermore, the known current coil has the disadvantage that the windings and tension relief loops at the connections can easily shift during transport and installation of the current coil so that the current coil can be easily damaged, which requires more care to be exercised in the transport and installation of the current coil into the needle motion sensor.
The current coil according to the invention, has an advantage over the prior art that the current coil can be automatically produced, automatically soldered, and then can be additionally extrusion coated so that all of the wires and windings are fixed in such a way that they can no longer move or be damaged during transport of the current coils or their installation into a needle motion sensor. The coil body of the current coil according to the invention has been provided with a particular wire guide, preferably the form of a formed groove, which permits the connecting contact wires that are preferably embodied as formed wire to be pressed into this formed groove. Due to the shaping of the formed groove, preferably as a groove profile, permits the connecting contact wire can be fixed immediately upon insertion into the formed groove. The shape of the connecting contact wire thereby produces a secure fixing in all directions and permits high securing forces to be achieved. The connecting contact wires are each provided with a tension relief loop and are inserted into the formed groove, which preferably is embedded completely in the coil body and permits a length compensation of the connecting contact wire. Another tension relief loop is advantageously provided at the ends of the coil winding wire before it is fastened to the connecting contact wire. These ends of the coil winding wire are advantageously guided to fixing lugs of the coil body. The connecting section between the ends of the coil winding wire to the connecting contact wires takes place by their being guided in a corresponding groove that extends obliquely to the axis of the coil body. In order to completely fix the wires in position and to secure them against an unintended movement, the coil body is also encompassed with a plastic material, preferably a hot glue.
In a particularly advantageous manner, the current coil according to the invention can be produced in an automated fashion. The connecting contact wires, which are embodied as formed wires, are first pressed into the corresponding formed grooves on the coil body with a tension relief loop and with radially protruding wire ends. In another process step, the coil wire is then automatically wound, wherein the coil wire beginning and the coil wire end are wound by the winding machine onto the radially protruding ends of the connecting contact wires. In another process step, the two wire ends are preferably soldered to each other in a solder bath. Then the connecting contact wire ends are bent inward toward the coil body. This produces the relief loops at the ends of the coil winding wire, which are each aligned with a fixing lug and are fixed. In another work step, the current coil is then completely extrusion coated with a plastic material, preferably hot glue.
This new manufacturing process for current coils has the advantage that the manufacturing process, which can now be automated, can achieve a degree of high manufacturing reliability. Furthermore, in particular the soldering process by means of immersion is especially advantageous. The additional extrusion coating of the current coil with a plastic also produces a high degree of security against unintentional changes to the winding wire position during transport or installation of the current coil. In addition, the closed plastic cover offers an additional protection of the coil region and the soldering points from damaging environmental influences.
Other advantages and advantageous embodiments of the subject of the invention can be inferred the from the drawings, the description, and the claims.